feat(mt): move worker trace policy to Rust

Move the first-job versus continuation-job trace policy out of the C worker
callback. Rust now decides when the external-dictionary assertion is required
and orders it before the trace, while C retains the private window assertion
and trace-recording leaves.

Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo check --tests
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --tests -- -A clippy::manual-bits -D warnings
- ulimit -v 41943040; make -j1
- ulimit -v 41943040; make -j1 -C tests test

lib/compress/zstdmt_compress.c

@@ -362,6 +362,24 @@ typedef char ZSTDMT_compression_job_finish_projection_layout[
                    + sizeof(ZSTDMT_RustCompressionJobFinishPublicationProjection))
         ? 1 : -1];
 
+typedef struct {
+    void* callbackContext;
+    unsigned firstJob;
+    ZSTDMT_compressionJobVoidFn assertNoExtDict;
+    ZSTDMT_compressionJobVoidFn trace;
+} ZSTDMT_RustCompressionJobTraceProjection;
+typedef char ZSTDMT_compression_job_trace_projection_layout[
+        (offsetof(ZSTDMT_RustCompressionJobTraceProjection, callbackContext) == 0
+         && offsetof(ZSTDMT_RustCompressionJobTraceProjection, firstJob)
+                == sizeof(void*)
+         && offsetof(ZSTDMT_RustCompressionJobTraceProjection, assertNoExtDict)
+                == 2 * sizeof(void*)
+         && offsetof(ZSTDMT_RustCompressionJobTraceProjection, trace)
+                == 3 * sizeof(void*)
+         && sizeof(ZSTDMT_RustCompressionJobTraceProjection)
+                == 4 * sizeof(void*))
+        ? 1 : -1];
+
 typedef struct {
     int checksumFlag;
     int ldmEnable;
@@ -422,6 +440,8 @@ void ZSTDMT_rust_compressionJob(
         ZSTDMT_compressionJobApplySequencesFn applySequences,
         ZSTDMT_compressionJobCompressFn compressJob,
         ZSTDMT_compressionJobVoidFn traceJob);
+void ZSTDMT_rust_compressionJobTrace(
+        const ZSTDMT_RustCompressionJobTraceProjection* projection);
 
 ZSTDMT_chunkProcessResult ZSTDMT_rust_compressJobChunks(
         ZSTD_CCtx* cctx, const void* src, size_t srcSize,
@@ -2247,18 +2267,34 @@ static ZSTDMT_chunkProcessResult ZSTDMT_compressionJobCompress(
         &progress, ZSTDMT_rust_compressionJobProgress);
 }
 
+static void ZSTDMT_compressionJobTraceAssertNoExtDict(void* opaque)
+{
+    ZSTDMT_compressionJobState* const state =
+        (ZSTDMT_compressionJobState*)opaque;
+
+    /* Double check that we don't have an ext-dict, because then our repcode
+     * invalidation doesn't work. */
+    assert(!ZSTD_window_hasExtDict(state->cctx->blockState.matchState.window));
+}
+
+static void ZSTDMT_compressionJobTraceRecord(void* opaque)
+{
+    ZSTDMT_compressionJobState* const state =
+        (ZSTDMT_compressionJobState*)opaque;
+    ZSTD_CCtx_trace(state->cctx, 0);
+}
+
 static void ZSTDMT_compressionJobTrace(void* opaque)
 {
     ZSTDMT_compressionJobState* const state =
         (ZSTDMT_compressionJobState*)opaque;
-    ZSTDMT_jobDescription* const job = state->job;
-
-    if (!job->firstJob) {
-        /* Double check that we don't have an ext-dict, because then our
-         * repcode invalidation doesn't work. */
-        assert(!ZSTD_window_hasExtDict(state->cctx->blockState.matchState.window));
-    }
-    ZSTD_CCtx_trace(state->cctx, 0);
+    ZSTDMT_RustCompressionJobTraceProjection const projection = {
+        state,
+        state->job->firstJob,
+        ZSTDMT_compressionJobTraceAssertNoExtDict,
+        ZSTDMT_compressionJobTraceRecord
+    };
+    ZSTDMT_rust_compressionJobTrace(&projection);
 }
 
 static void ZSTDMT_compressionJobEnsureFinished(void* opaque)